Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$17.82	4.250%	$18.5774	$18.58	$18.60	$18.60
Purchase #2	$92.42	4.746%	$96.8063	$96.81	$96.80	$96.80
Purchase #3	$17.58	10.190%	$19.3714	$19.37	$19.35	$19.40
Purchase #4	$30.58	9.459%	$33.4726	$33.47	$33.45	$33.50
Purchase #5	$132.35	13.374%	$150.0505	$150.05	$150.05	$150.10
Purchase #6	$132.47	7.608%	$142.5483	$142.55	$142.55	$142.50
Purchase #7	$61.31	9.255%	$66.9842	$66.98	$67.00	$67.00
7 purchase totals =	$484.53		$527.8107	$527.81	$527.80	$527.90